The application relates to a hand-held work implement having a braking device and a process for producing the braking device as set forth herein. In an exemplary embodiment of the hand-held work implement, the hand-held work implement has a tool and a braking device for the tool. The braking device itself includes a brake band, which wraps around a brake drum, and the brake band and the brake drum form a first part and a second part undergoing friction. The first part and second part undergoing friction move relative to one another during the braking operation. The first part undergoing friction is an austenitic steel, a duplex steel, super duplex steel, a nickel-base alloy or a cobalt-base alloy and has a base body and a marginal layer. The hardness of the marginal layer is approximately 150% to approximately 600% of the hardness of the base body and the carbide proportion in the marginal layer is less than approximately 0.5% by weight.
In an exemplary embodiment of a process for producing the braking device for the hand-held work implement, carbon and/or nitrogen is made to diffuse into a marginal layer of the first part undergoing friction at a temperature of less than 500° C.
It is known from DE 38 02 488 A1 to coat brake bands, which can serve, for example, for stopping the saw chain of a power saw. The coating can be effected, for example, with aluminum oxide in a plasma coating process. On account of such a coating of the brake band, it is possible to realize short braking times combined with a high service life of the brake band. However, a coating of this type is relatively complex and therefore expensive.
DE 195 81 791 B4 discloses a frictional pairing for a synchronizing device in gear change transmissions, in which one of the parts undergoing friction is a ferritic or austenitic steel with a high chromium content and a carbide-rich zone comprising at least 30% by volume carbides. It is also provided to carburize the two parts undergoing friction at 1050° C. in an oxygen-free atmosphere. Chromium mixed carbides thereby form in the layer close to the surface. Components having a carburized surface are brittle. A brake band of a braking device of a hand-held work implement having such a surface might break during operation, since, on account of the severe heating of the brake band during the braking operation, austenitization repeatedly occurs during operation, as a result of which the brake band is embrittled.
From DE 10 2004 060 016 A1, it is also known, for a frictional pairing, to treat one of the parts undergoing friction initially by a hardening process, such as case hardening. Case hardening, too, is usually effected at very high temperatures of above 900° C.
The brochure entitled “Kolsterisieren” [Kolsterizing] from Bodycote Hardiff BV, Apeldoorn, The Netherlands discloses a process for surface hardening austenitic, stainless steel, in which carbon is made to diffuse into the surface of the material at low temperatures. In this process, no carbides are formed. The “kolsterized” surface is intended to have an increased wear resistance and avoid fretting at sliding surfaces. The tendency toward adhesion is to be reduced.
One object of the present application is to provide a hand-held work implement of the generic type, the braking device of which has a high service life and affords good braking results. Another object of the invention to specify a process for producing a braking device of a hand-held work implement which has a high service life and achieves short braking times.